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There are quit a few companies producing kits for metal frame buildings now. I’ll find some links and post a few. I’ll list a few types below.
- Square or Rectangular with Gable, Leanto or Near Flat roofs
- Lean-to all the way to ground level (like a half A-Frame)
- Half Cylinder, Half round, or Quonset Hut (like Gomer Pile Marine Barracks)
- Silo shape, Like Mongolian Yurt or Grain Silo
- Geodesic Dome (Made up of a framework of triangles which form a half sphere shape)
- Dome Half Sphere vertical ribs
- Dome Half Sphere horizontal ribs
- Ocean Sea Container
In this article I will mostly talk about some ideas that I have for small simple metal buildings made from scrap angle iron or metals. I feel that I could construct a frame from scrap for something to cover less than 400 square feet(37m2) of floor space without needing an engineer or architect if I do some research first and think through my design carefully. I would also not span distances of more than 16 feet (5m). With the kind and sizes of scrap most of us have available in today’s world, buildings of this size should be safe enough. Though you might consider occupancy in your safety considerations. For example A shop is occupied part of the time. A storage shelter rarely. A home or living space possibly daily. The more serious the occupancy application, then the more rigorous thought that goes into the engineering requirements. As another example if snow and ice buildup might be a concern then don’t occupy your building when snow and ice is on it. If wind was a concern then don’t expect to have to occupy it during wind storms and hurricanes. Nothing replaces the added confidence in money spent on structural engineering however. Though even engineers in their calculations consider occupancy and beef up the engineering based on seriousness of occupancy. You just have to be careful enough with the “beefing” or you will create a structure that can’t hold itself up.
If I can find some info about the relative strength of some I-Beam or simple truss designs that will span 16 feet (5m) or less I’ll post them here. As far as roof weight goes, we are talking about mostly snow weight possibly combined with wind. Though a flat sod covered roof needs to support 200 lbs per square foot (90kg) or (1000kg per m2) which doesn’t count the weight of the structure itself. A steep roof with slick roofing material which might be heated part of the time would not be as worrisome as a lesser sloped roof with rough roofing and no heat. The dome’s and half rounds would be less worrisome in my opinion because they would hold up less snow or ice. Round shapes seem to be much better at handling wind as well. The A-Frame would be less worrisome because of its steep roof (for ice or snow) though it kind of sets up like a leaning sail for the wind from 2 directions. For wind a 45 degree sloped (12:12 pitch) A-Frame might be best.
None the less pay close attention to other metal buildings in your area where you may inspect the framework. Note the types of metal, shapes of members and thicknesses of members. In some cases you might want to overkill on bracing and with support poles or tie beams to make up for lack of engineering. Though note that extra weight in roof structure could be a problem. One advantage of metal frames is that they eliminate the need for support poles in spans where wood requires it. 400 ft2 of floor space in rectangular would be 20′x20′(6mx6m) or 10′x40′(3mx12m). 400 ft2 in round would be 22′(3.2m) in diameter and about 75′ (22m) in circumference. If you have any doubts search out a structural engineer. Also the businesses that produce metal buildings might work up some plans for you cheaply. They have engineers on the payroll and use software specially designed for metal building architecture. On a side note, when commercial poultry producers first began using metal frames which would span 40 (12m) to 50 (15m) feet without poles, some collapsed due to snow weight the first few winters in the southern USA area. Even engineers make mistakes. In this case I’m sure it was due to pressure to save on construction cost because of building competition.
I have no intention of making up the square framed metal buildings from scrap metal. If I did it would only be very small structures and probably only for storage, animal shelters, or rain sheds. I will post some links to some sites that design and sell kits after I get time to look some up. Forgive me for the crude sketching, I’m sure it leaves a lot to be desired. My sketching is better than nothing though and at least it gives the reader a hint as to what I’m talking about in this article.
A-frame, vs more conventional box designs, has a much steeper roof and will not hold snow or ice or will shed the snow or ice more quickly, especially if the roofing material is slick and possibly heated from underneath. Lean-to is another example for an easy design for DIY. A Lean-to where the roofing is steep and comes to the ground or nearly to the ground is somewhat like a half a-frame. On a side note a pyramid shape would be like crossing an A-Frame with a Hip Roof design. I have seen some large pyramid shaped metal buildings around the country in industry. I was unable to determine what they were used for exactly though.
I have seen several types of (half cylinder/half round/Quonset hut) shaped buildings in use around the USA. I will look up some manufacturers of kits for these as well. They come in different types of corrugated roofing. But I’d say this shape is more ideal for the home made building made from scrap because of simplicity alone. The ones I see usually have the corrugations rows following the arches. In some cases the corrugated and metal alone is strong enough to support itself. I have seen two types of corrugation. One is accordion like V shapes. The other is like a true S or sine wave shape. If the corrugation parallels the arches(hoops) then the metal must be pre-made in a circular shape, similar to the metal used on grain silos and culverts. On the homemade version of this note how easily the old corrugated roofing tin will fold down and over this if the corrugations cross the arches(hoops). It would not be difficult to shingle half round in some way with any flat metal you can come up with. For example No. 10 can’s made into shingles.
There might be two ways to make a set of half circle ribs for this type. One would be pipe bent with a pipe bending machine to the perfect curve for the size of building being made. Angle iron could then be used as stringers going between the half pipe-hoops. This is similar to the pvc poly tunnel construction for quick and dirty green houses for gardening plants. Corrugated metal roofing would be perfect for this where the rows of the corrugations would be parallel to the length of the structure. This metal roofing would bend easily over the structure and frame. Caulking and proper overlapping would be required. Screws with washers and rubber seal washers would be used to fasten the roofing to the frame.
The second type of frame would use a half perfect polygon shape where a number of angled bends would be made in a piece of angle iron. At each angle one side would be cut downward to meet the 90 degree bend so that you would only be bending one side which is flat. Then there would be a small amount of overlap at the bend on the side that was cut where it could be welded together. Again angle iron would be used as stringers. Same roofing method as the first. And actually angles could bent in pipe at given distances for the same effect by using hand operated pipe bending equipment.
Lets say that you want to figure the angles and distance between angles for the bends. Simply divided 360 by the number of angles in the circle (even number so that one angle ends up at the very top). Draw on a piece of graph paper a Circle representing the full or half circle shape of the half hoop (rib). Next draw a line from the center of the circle 90 degrees to the top of the rib. Then draw and array of lines all the way down on both sides along the circle from the center using the calculated angle from above between each line. Next draw lines from bend point(where each line touches the circle) to bend point around the circle inside it. You may now measure the distance between angles and angles of the bends themselves. I will try to post some diagrams for these two types soon. One other idea is to take a grain or feed bin and cut it in half, viola, instant roofing. And what about giant corrugated culverts?
Below is a calculator that would help you in the design of a frame for a half round, vertical axis dome, horizontal axis dome frame. Click the image below to bring up the calculator. You will enter the number of bends in the frame. You will also enter the radius of the frame in “units” not feet or meters, so that it can represent feet or meters. This is the number for a full circle. So half that number or less would be for the top half of your typical half round or dome structure. The yellow line indicates the number of angles and sides above ground level. It shows half the distance of the perfect polygon which will be the total length of all the members of the rib. It also gives the length of the rib pieces between angles and the angle between rib pieces. As you can see, the more angles or sides you have the rounder the structure will become. However more round means more work involved in constructing each rib. This could be used for metal, plastic or wood frames, or any combination of materials. However do not use this for engineering but only for design purposes. If you have any doubts seek out a qualified structural engineer.
The “clickable” calculator (Polygon Calculator) above can also help you to determine the angles and lengths for metal pieces needed in a cone shaped roof such as the Silo/Yurt type roof below. These metal pieces might be overlapped or be put together as a standing seam roof. For the calculations though use the distance from the edge of the roof to the peak for the radius, not the actual horizontal distance. For example the radius above was 8, but if you used right triangle math to figure a hypotenuse for a rise of five feet then you would need to resupply the radius as the sloped distance of around 10 or 12 feet. This would give you proper angles between pieces and lengths at the bottom of the slope. Anyway it you use your imagination a bit, this calculator will work out for you for this purpose as well.
Feed bins, Grain Silo’s and the Mongolian Yurt Shape are all basically the same. You have a vertical wall shaped like a cylinder standing up, with a cone shaped roof. I will be looking up some manufacturers for feed bins and grain silo’s to post here. For the home made version why not use the design from the Yurt. Flat or angle iron could be used for the sides. But at least one of the directions of the roof lattice would need to be angle iron for strength if not both. Built to the wooden yurt specks I’d say this will be far more than strong enough to hold up a bit of ice and snow. I’m not saying use solid steel that is 1×2 (2.5cm x 5cm) or 1×3 (2.5cm x 7.5cm) but tubular, U shape or angle iron with those dimensions. Wind would be no problem with a frame like this. Guy wires would probably not be needed as they are for the wooden frame yurt. On a metal frame like this square doors could be designed into it instead of coffin shaped doors. I would roof this with flat tin or sheet metal with standing seams. I actually found a chapter in a book on standing seam roofs that was pretty good. The book however was about square log homes called “The Hewn Log House”. Each piece of the yurt standing seam roof would be like a piece of pie, where two pie pieces come together there is a standing seam. It could be bolted or screwed down at the top around the compression ring area. Again if you were really concerned about roof support, a ladder could be made in the middle that would run to the sky light at the top and would brace the roof with pole like support. Corrugated sheet metal could be used for the sides and as I said earlier it will bend nicely around the curved shape. In this case the rows of corrugations will be vertical.
Geodesic domes are a very strong structure made of triangles inside hexagons or pentagons. Search the web for geodesic dome frame calculators or use the one at Desert Domes They show exactly how to position the pieces and their lengths and angles. Angle iron, a welder and cutting torch will work nicely here. Keeping the thing shaped like a sphere is simple. Use stake in the center with a cord or rope attached and the rope should have a knot or stick tied at the distance of the radius of the structure. Just pull this taunt at each joint to make sure its in the right position before welding. If needed a torch can heat and bend something to the right position. A friend of mine at Minimal Intentions has some blog post about a metal geodesic dome frame he made from electrical conduit. He spent $300 for the conduit, cut and flattened ends, drilled holes and bolted the thing together. It spans 19′ (2.9m) and has around 350ft2 (33m2) of floor space. As a testament to its strength he sleeps on a trampoline that has been suspended about 8 feet above floor level with steel cables.
Roofing is another problem altogether and I personally don’t like asphalt shingles for geodesic. I’d suggest some kind of flat metal roofing but not corrugated unless it were very finely corrugated. If its flat sheet metal roofing I might consider welding, soldering or braising it to the frame, though this might be expensive, it would be long lasting. Caulking, screws, metal and rubber washers to fasten the roofing down. Roofing would probably be cut in triangular or hexagonal shapes. Could be cut in double triangular shapes as well. If you used Plexi Glass or glass for roofing then you would have an agri (agricultural or green house) dome. Sky lighting would be easy by using plexiglass for roofing a few of the triangles here and there. Pipe could be used instead angle iron and so could rebar. There are probably many variations on this theme. The dome forms a half sphere and it wouldn’t have to be set right on the ground. I could be set up on a partial or full circular wall or poles or whatever to get it up a bit higher for more head room.
There are two types of domes I found that are dissimilar to geodesic. Horizontal axis ribs and Vertical Axis Ribs. To imagine the horizontal axis ribs think of the old horse buggy with the folding cover or the convertible car and its folding cover. Note the ribs on these covers. For the vertical axis ribs think of the wire whips for whipping eggs and cream and potatoes that cooks use or maybe the umbrella. Though I have seen some whips that cooks use which are more like the Horizontal axis ribs. Another great example for the horizontal is that famous set of buildings in Sydney Australia that we see on movies a lot, and I can’t even tell you the name of the building. At any rate what I said above for the design and construction of the half round ribs will work for these two types of domes as well.
Sea Vans or Ocean containers are probably one of the easiest solutions to quick and dirty DIY housing that is rugged, durable, long lasting, and water tight. At the time of this writing I could get a 53 foot sea container brand new for $5000 to $8000. And they even come with nice looking wood floors in them! This would be one of the easiest methods for a non skilled builder to use in my opinion. And there are many many ways containers can be combined. They can be buried for underground housing, though probably not best to do this below grade or too deep. They can be bermed and earth roofed easily. You can weld metal structure to them or bolt it to them easily. I hear the corner areas are the strongest points for stacking these. Roofs can bow and sides are not necessarily strong even though they are corrugated. However stacked or just setting in the open would cause no alarm.
I show using the image at the top of the article an idea that I really badly want to try some day where I would take two 53 foot (15m) containers and put them side by side but spaced 16 feet (5m) apart. I would span them every 1.5 (.5m) feet with a beam of some kind to hold up an earth roof (which might require post support to be added to the end of each beam because of the earth roof weight, the containers themselves might not support the earth roof weight).
To support an earth roof of 300 ppsf there are two methods I recently heard about on a podcast. On is totally with wood on the inside. You use 4×4 pine post(studs). Place them every 4 feet just above a floor runner. Floor runners are on 12 inch centers in the floor of the ocean container for floor support. On top of the 4×4 use two 2×8 or 2×10 all the way down so that you have 4×8 or 4×10 on top of the 4×4 post. This comes to within 6″ of the metal ceiling. Then across you use 2×6 on 16″ centers placed on top of the 4″ ledge formed by the 4×8 or 4×10 bearing plate. This is adequate for holding up 300 ppsf which would be 4″ of Styrofoam insulation and 1 foot of earth and 6 feet of snow and water in the soil.
The next method requires welding. You get U shaped studs and weld them in every 4 feet. You then use a 2″x3″ piece of angle iron on each side. With 3″ horizontal for resting 2×6 boards on. Weld that in on each side. Next place your 2×6′s again on 16″ centers. Also your 2×6′s might need to be camphorred a bit with some trimming. This means making a slight arch shape to match the roofs slight arch shape for a tight fit.
Double pane non operable windows would go between each beam, with maybe an operable window here and there for ventilation. I would berm up to within 6 inches of the top of each container on the outside of this structure. I would sod roof the containers and the center roof with 6″ of earth and sod. I might extend the berm around the ends of the containers on all 4 ends (2 ends on each container) I’d cut a door in the middle of each container on the inside. Some kind of flooring on the inside and some type of end walls, with double doors on each end. A stove or fireplace for heat. I would cut some holes in the tops of the containers on the sides all the way around for very small windows for sun lighting. If you build up a pad a couple of feet for the containers to rest on then the floor in the central section could be 2 foot (2/3m) lower and give 2 more foot of head room. This would give 12 feet (3m) of head space in the center with 7.5 feet (1.5m) in the containers. This design would give 1500 square feet (140m2) of space in the structure.
As for the roof structure in the middle, if it were only a frame for holding up a metal roof that might not need too much support enhancements on the containers. If it were earth then you would need to support it with columns and bearing plate as we talked about on the inside. The corners of the containers take a lot of weight. But the sides need reinforcement.
Variants on this might be larger spans in the center (more well engineered) and containers on the sides double stacked for 2nd story rooms giving 20 foot(6m) of head room in the center. The 2nd story containers would not be bermed but would be well insulated. They would still have the sod roof on top and the sky light windows between beams all the way down.
There are many many many variation on how containers could be used for structures because they are made to be so strong for the rough trucking and ocean shipping business. You are only limited by the imagination. And they can be strength enhanced.
Other roofing for metal structures ideas could be in the use of papercrete, gunite, shotcrete and plasters. Plasters could be made lighter with the use of something like vermiculite instead of sand in the mix. And I’m sure there are many other options once one gets to looking into it. Certainly canvas for the half cylinders would be a snap, since its a mere rectangle. Plastics as well.
There could be a huge list of tools that would go well with this article. But I will only mention a few below.
- Sheet Metal Brake (not necessary and might not be cheap)
- Metal Brake (not necessary and might not be cheap and may require 3 phase electricity)
- Oxy- acetylene Cutting Torch and Welding Torch.
- Arc Welder
- Other types of welders, cutters.
- Drills and metal bits
- Wrenches, Sockets, Ratchets
- Pipe Bending tools
List of tools for working standing seam metal roofing.
- Duckbill vice grips
- Seaming Iron
- Wooden Mallet
- Roofing Tongs
Below is a table of metal strengths. These are approximated so use them for thinking about design but not for actual engineering. For actual engineering you would use numbers for the specific exact metal type and situation from the Machinery’s Handbook, in the Strengths of materials section. Yield Strength is basically bending to the point of plastic deformation. Whereas Elasticity is bending to a point where it can snap back into original shape. This can also be known as deflection or springiness. The values are PSI (Pounds per square Inch)
|Cast Iron||20,000 to
|Carbon Steel||60,000 to216,000||60,000 to216,000||45,000 to160,000||40,000 to150,000||30,000,000||11,500,000|
|Steel Alloys||80,000 to285,000||80,000 to285,000||60,000 to214,000||25,000 to228,000||30,000,000||11,500,000|
|Stainless steel||70,000 to230,000||70,000 to230,000||None||30,000 to195,000||28,000,000 to29,000,000||13,000,000 to14,000,000|
|Aluminum Alloys||10,000 to110,000||10,000 to110,000||7,000 to48,000||8,000 to23,000||10,000 to18,000||None|
How might you use these values above? I mean we all knew that metal is hard and strong. I’m not an engineer so this will be a discussion from an apprentice or students point of view. We have to learn about these forces and how they act on the materials. We also have to be able to imagine simple situations within more complex situations. I talk more about engineering in the article Timber Frame, Post and Beam, Beam and Stringer and you may want to read this as a perquisite for this article. For this DIY metal building stuff I’d say as anyone else would as well, KISS principle , Keep It Simple Stupid.
Lets say you want to roof an area between two ocean containers as in my above idea and example. Lets also assume that the containers are strong enough to support the weight for example purposes. Lets use 20′ containers and shorten the distance between them to 10′. In a flat system you call the beams that span between the containers rafters or joist. On top of the rafters would be stringers running perpendicular. This forms a grid skeletal framework which would support roofing material and anything that ends up on top of the roofing material, such as snow, ice, debris etc. We would calculated first weight on a tributary areas. If our rafters were spaced out at 2 feet and 2 feet between stringers, a tributary area might be 2′x2′. So there would be 50 of these areas combined in the total roof space. You could figure weight on each stringer and then each rafter in the 2×2 area. Then total for the roof. Half of that weight will be on one container, and half on the other. You could then figure weight per linear foot along the top of each container.
Typically you would use angle iron, tube iron, I beams and possibly flat iron strips for the stringers. Lets keep it even simpler than that and use solid square rods for both stringers and rafters. Though you could probably find 1″ tube steel with strength properties of our example here which is using solid rods. Span is important when considering bending. When a member is being bent, say from above, you develop compression forces on top of the member and tension forces underneath it. Lets say you push down with 200 pounds force on our beam that is spanning 10 feet. This will generate a certain amount of compression and tension based on the span of 10 feet. If we stretch that span out to 20 feet then you can see that even with the same weight the compression and tension forces increase greatly. Whether or not this increase is double or far more than double I don’t know yet. If these stresses reach the PSI limits above for the given metal type, then permanent bending or (yielding or plastic deformation) occurs. If not then springy type bending called deflection can occur.
From the table above you can see that we can have up to 45,000 psi in shear weight for carbon steel before the rafters will break/shear. In our roof example so far we might have 200lbs per ft2 (far greater than a normal roof, this might be a weight for a sod earth roof with 5 feet of snow on top) which translates to 400lbs per linear foot on the stringers. or 800lbs on the point of contact between the stringer and the rafter. Since in our simple example our stringers and rafters are 1″x1″ this means the roof weight alone is only 800 psi on the rafter. This is well below the shear strength of the rafter member. Added to this 800PSI will also be the weight of the stringer member 2 feet long. The Machinery’s Handbook can tell you this weight in its sections on weights of materials. For arguments sake lets guess that the steel 1×1 member weights 3.5lbs per linear foot more or less. This brings the psi up to 807psi.
We can not span any length we want with our 1×1 rafters. If we keep increasing the length of the span eventually it will sag and even collapse. We need to know based on 10 foot span what kind of weight it will support without bending. We have 807lbs every 2 feet plus the weight of the rafter which is 3.5lbs per linear foot. Dividing the 807/2 gives 403.5lbs per linear foot plus 3.5 lbs or 407 lbs per linear foot. And 4,070 pounds per rafter. 10 rafters gives us 40,700 lbs for the entire roof. Which is 20,350 lbs on each sea container. We could distribute this weight down the length of the container to be 2,035 lbs per linear foot. Translate this to psi on the rafter to container and we get 4,070 psi. That won’t shear the rafter.
Engineers Edge Web site Has some formula’s we may use. The bending formula says bending stress = (3 x load x length)/(2 x width x (thickness x thickness)). I wish I understood how they came by this formula but I don’t. Our load will be 407 lbs. Our length is 10 feet or 120 inches. (3x407x120)/(2x1x(1×1)) or 73,260. Looking at the carbon steel chart above lower end strengths are 60,000 for tensile and compression. If we are correct here that means our roof might be too heavy. If we shorten the span to 8 feet then we get 58,608 from the formula. This seems acceptable. There are many ways to change this so that it would work out. There are many ways we could change the situation to make it work out. We could add intermediate support post and/or bracing. The member sizes will need to be increased to larger than 1×1. We could space the rafters closer together such as 1.5 feet instead of 2 feet. Also if we were not doing a sod roof then we could reduce the roof load to normal roof loads. We could also change the metal type to something that is both known and stronger. There are carbon steels that are stronger than the weakest ratings in the above table.
A person could certainly make up a spreadsheet to calculate these figures for them quit easily. Then to design a different sized roof system all that is needed is to alter a few key values. For a free spreadsheet Google for “Open Office” and I think their spreadsheet is called “Calc”.
I didn’t talk about fastening anything. If we welded the grid frame it would add a lot of strength. It would also add to cost and time. But remember a good weld is stronger than the metals being welded. I have no info to give you on bolting, though you could make brackets to go around the 1″ steel bars.
There are 3 to 4 methods for engineering anything that I have found so far. One is by using math and calculations. The other is by using tables for values and codes for guidelines and is called Prescribed method. These tables have been calculated based on materials testing and engineering formulas. Then there is the empirical method. Empirical is like wind tunnel testing. Finally if you count it the 4th method is in cloning (copying, borrowing or reverse engineering which is also a form of prescribed methods). In our simple example above we can find formulas and strength data and crunch the numbers. We can find code books with tables and use that as a guide. We can build it then stand on it and jump up and down on it to see if it holds up. Or we can find an example in our neighborhood that is spanning the same distance and copy the member sizes and spacings, using the same materials and member shapes and dimensions.
If you acquire materials from the manufacturer then they can tell you the stresses in the tables above concerning the exact product you buy. For example square tubing. Then you may use all the methods above to determine if your design will hold up base on the manufacturer ratings. If we are using scrap then we have to use some real common sense and experience and do a bit of investigation so that we can determine minimum strength properties.
If we calculated a flat roof with the same area as an A-Frame, Lean-to or Half-Round roof, it most likely would work fine. This is because the actual loads would be less for those designs.
|Machinery’s HandbookErik Oberg, Franklin D Jones, Henry H Ryffel and Christopher J McCauley